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Subject[PATCH] mm/shmem: set default tmpfs size according to memcg limit
Date
Currently the default tmpfs size is totalram_pages / 2 if mount tmpfs
without "-o size=XXX".
When we mount tmpfs in a container(i.e. docker), it is also
totalram_pages / 2 regardless of the memory limit on this container.
That may easily cause OOM if tmpfs occupied too much memory when swap is
off.
So when we mount tmpfs in a memcg, the default size should be limited by
the memcg memory.limit.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
---
include/linux/memcontrol.h | 1 +
mm/memcontrol.c | 2 +-
mm/shmem.c | 20 +++++++++++++++++++-
3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 69966c4..79c6709 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -265,6 +265,7 @@ struct mem_cgroup {
/* WARNING: nodeinfo must be the last member here */
};

+extern struct mutex memcg_limit_mutex;
extern struct mem_cgroup *root_mem_cgroup;

static inline bool mem_cgroup_disabled(void)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 661f046..ad32f3c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2464,7 +2464,7 @@ static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
}
#endif

-static DEFINE_MUTEX(memcg_limit_mutex);
+DEFINE_MUTEX(memcg_limit_mutex);

static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
unsigned long limit)
diff --git a/mm/shmem.c b/mm/shmem.c
index 07a1d22..1c320dd 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -35,6 +35,7 @@
#include <linux/uio.h>
#include <linux/khugepaged.h>
#include <linux/hugetlb.h>
+#include <linux/memcontrol.h>

#include <asm/tlbflush.h> /* for arch/microblaze update_mmu_cache() */

@@ -108,7 +109,24 @@ struct shmem_falloc {
#ifdef CONFIG_TMPFS
static unsigned long shmem_default_max_blocks(void)
{
- return totalram_pages / 2;
+ unsigned long size;
+
+#ifdef CONFIG_MEMCG
+ struct mem_cgroup *memcg = mem_cgroup_from_task(current);
+
+ if (memcg == NULL || memcg == root_mem_cgroup)
+ size = totalram_pages / 2;
+ else {
+ mutex_lock(&memcg_limit_mutex);
+ size = memcg->memory.limit > totalram_pages ?
+ totalram_pages / 2 : memcg->memory.limit / 2;
+ mutex_unlock(&memcg_limit_mutex);
+ }
+#else
+ size = totalram_pages / 2;
+#endif
+
+ return size;
}

static unsigned long shmem_default_max_inodes(void)
--
1.8.3.1
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